Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://xmm.vilspa.esa.es/docs/documents/CAL-TN-0082.pdf Äàòà èçìåíåíèÿ: Tue Apr 14 17:50:20 2009 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 20:46:00 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: meteoroid

XMM-Newton SOC Technical Note
XMM-SOC-CAL-TN-0082 Accuracy of energy reconstruction in EPIC-MOS Timing Mo de
M. Guainazzi April 6, 2009

History
Version 1.0 Date April 6, 2009 Editor M.Guainazzi Note SASv8.0

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Motivation and metho dology

In the rep ort I study the accuracy of the energy reconstruction in EPIC-MOS Timing Mo de. For this purp ose I analyzed the sp ectra of two bright, line-rich Sup erNova Remnants (SNRs: Cas A, and N132D) observed b efore the micro-meteoroid impact in Rev.#961 (Guainazzi 2009). The centroid energy of the strongest emission lines measured in these sp ectra has b een compared with that simultaneously measured by EPIC-pn Full Frame exp osures and with exp osures of the same targets taken in MOS imaging mo des (Full Frame and Large Window; Sect. 3.1). The nominal energy reconstruction accuracy in imaging mo des is ±10 eV for the three EPIC cameras over their whole sensitive bandpass (Guainazzi 2009). Furthermore, the b est-fit phenomenological mo del for the RGS sp ectra of the star AU Microscopii (Rev.#155) has b een compared with a simultaneous MOS2 Timing Mo de sp ectrum, to cross-check that the results obtained with the aforementioned reference targets are not affected by the extended nature of their X-ray emission.

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Data reduction

Table 1 shows the list of observations discussed in this rep ort. In Obs.#0129341101 and #0165560101 Table 1: List of observations discussed in this rep ort Source N132D N132D N132D CasA CasA AU Microscopii
a

Obs.# 0129341101 0210681301 0157160301 0165560101 0097610501 0111420101

MOS mo de Timing Full Frame Large Window Timing Large Window Timinga

only MOS2

the EPIC-MOS cameras were op erated in Timing Mo de, while the EPIC-pn camera was op erated in Full Frame Mo de. Given the large extension of these sources (>1') the pile-up fraction is negligible in all exp osures [Bleeker et al. (2001) estimate an EPIC-pn pile-up fraction <3% in the brightest knots of Cas A, for instance]. Data were reduced with SASv8.0 (Gabriel et al. 2003) 1 , using the most up dated calibration files available at the date of the rep ort's publication. Standard screening criteria were applied to the data, as defined by the #XMMEA EM and FLAG==0 selectlib expressions for EPIC-MOS and EPIC-pn, resp ectively. Single-events EPIC-pn time-averaged sp ectra were accumulated from circular regions around the apparent centroid of the X-ray source. EPIC-MOS Timing Mo de time-averaged sp ectra
The Release Note for this SAS version is available at the http://xmm2.esac.esa.int/sas/8.0.0/documentation/releasenotes/xmmsas 8.0.0.shtml
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following

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Table 2: Count rates and extraction regions for the observations discussed in this rep ort. The MOS Timing Mo de extraction regions are expressed in detector co ordinate ranges (extrema included); the imaging mo des extraction regions are circles centered around the apparent centroid of the X-ray image.
Source N132D Cas A AU Mic
a

Count rates (s-1 MOS 1 MOS 2a 18.14 ± 0.04 24.02 ± 0.04 76.01 ± 0.08 53.06 ± 0.07 ... 2.852 ± 0.007
a

) pn/RGS 77.59 ± 0.10 251.5 ± 0.2 0.612 ± 0.003

Extraction region ranges MOS 1a (RAWX) MOS 2a (RAWX) 270-345 270-345 255-324 278-346 ... 288-315

pn 80 240 ...

radii (") MOSb (FF/LW) 140/120 250/170 ..

Timing Mo de; b imaging mo des.
1000
MgXII SXV CaXIX ArXVII NiXXVII FeXXIII

1000

CasA - Obs.#0165560101
SiXIII SiXIV SiXIII SiXVI

N132D - Obs.#0129341101
OVII OVIII NeIX NeX MgXI SiXIII SXV ArXVII MgXII SiXIV

100

Cts s-1 keV-1

Cts s-1 keV-1 0.5 1 2 Energy (keV) 5

10

1

0.1

0.01

0.01

0.1 0.5

1

10

100

1

2 Energy (keV)

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Figure 1: The EPIC sp ectra of Cas A (left) and N132D (right) discussed in this rep ort. The dashed lines indicate the lab oratory energies of the transitions used in this rep ort. Black: MOS1; red: MOS2; green: pn. were accumulated from ranges in RAWX. Sp ectra from the EPIC-MOS exp osures in imaging mo de were accumulated using the standard combination of single and double events (PATTERN <= 12) to maximize the signal-to-noise ratio. In Tab. 2 the size of the sp ectral extraction regions as well as the count rate in the energy range used for the sp ectral analysis (see later) is rep orted. Sp ectra have b een analyzed in the 0.5-8 keV and 0.5-5 keV energy bands for Cas A and N132D, resp ectively. This ranges are smaller than the recommended energy range where EPIC-MOS sp ectra in Timing Mo de are nominally calibrated (0.3­10 keV; see Fig. 1). They have b een chosen in order to simplify the sp ectral mo deling of these sources, by excluding energy ranges with p o or signal-to-noise ratio or no detected emission lines. I mo deled the sp ectra with the combination of two bremsstrahlung continua and as many Gaussian profiles as statistically required by the fit at a confidence level larger than 90% for one interesting parameter according to the F-test. The same confidence level is used to define the statistical errors on the centroid energies in this rep ort. The sp ectra are shown in Fig. 1, where the dashed lines indicate the lab oratory energy of the atomic transitions used in this rep ort, according to the ATOMDB database (available at: http://xcx.harvard.edu/atomdb). The RGS sp ectra of AU Microscopii were extracted with rgsproc. Background sp ectra were


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Figure 2: Difference left) and p ercentage difference (right) b etween the centroid energies measured by the EPIC-MOS cameras (MOS 1: top; MOS 2: bottom) in Timing Mo de and the EPIC-pn (Full Frame) as a function of the centroid energy as measured by the EPIC-pn. Empty (Fil led) circles corresp ond to the N132D (Cas A) measurements. The dashed-dotted lines mark the ±10 eV and ±30 eV lo cus around the EPIC-pn energy. Only data p oints are shown, whose relative statistical error is smaller than 25% on b oth the pn and the MOS cameras. accumulated from standard offset p ositions of the observation field-of-view. The reference sky p osition for the asp ect solution was set equal to the SIMBAD source co ordinates: 2000 = 20 45'09".5, 2000 = -31h 20m 27s . The 0.3­2 keV RGS sp ectrum was fit with a combination of 1 thermal bremsstrahlung and 17 Gaussian lines (see App endix A).

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3.1

Results
EPIC camera cross-calibration

In Fig. 2 I show the discrepancy b etween the energy measured by the MOS cameras in Timing Mo de and simultaneous exp osures of the same targets in pn Full Frame mo de. These discrepancies are expressed either as the energy difference or as a p ercentage difference ( EM OS -Epn ) b etween the Epn b est-fit centroid energies. In Table 1 the mean and standard deviation of the energy differences are rep orted p er camera and observation. At the 1- level they are 30 eV and 20 eV (basically camera-indep endent) for the N132D and CasA observations, resp ectively. Fig. 3 shows the same typ e of plot as in Fig. 2 for a comparison b etween MOS exp osures in imaging and Timing mo des. At the 1- level they are 30 eV and and 20 eV (basically camera-indep endent) for the N132D and CasA observations, resp ectively. Interestingly enough, the discrepancy has got opposite signs in N132D and CasA.


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Table 3: Mean and standard deviation (in eV) of the b est-fit centroid energy differences measured by EPIC-MOS in Timing and imaging mo des, and pn in Full Frame Mo de Exp eriment N132D CasA pn vs. MOS1 12 ± 13 8 ± 12 pn vs. MOS2 15 ± 18 4 ± 17 MOS1 imaging versus Timing mo des 11 ± 16 -16 ± 8 MOS2 imaging versus Timing mo des 10 ± 8 -7 ± 4

Figure 3: The same plot as in Fig. 2 when MOS exp osures in imaging and Timing mo des are compared. Different targets and mo des are color coded.


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5

Cts s-1 keV

-1

Data/model ratio

0.5

1

1.5

21

2 1

5 2

0.5

Energy (keV)

1

Figure 4: Left panel: RGS combined sp ectra of AU Microscopii (from BiRD; Gonz´ alez-Riestra & Ro dr´ iguez-Pascual 2008); Right panel: MOS 2 sp ectrum (upper panel) and residuals in data/mo del ratio (lower panel) against the b est-fit RGS mo del. The colors lab el the fit with: no gain shifting (red); constant offset gain (black); or linear gain shift (blue). Table 4: Parameters of the gain fit Xspec command applied to the MOS 2 sp ectrum of AU Microscopii when the b est-fit RGS mo del is applied. Offset (eV) 18.3±0.7 18.8 ± 0.4 0.3 Slop e 1f ixed 1.00219±0.00024 0.00007 MOS 2/RGS 1 normalization 97.8 ± 0.5% 98.0 ± 0.4 % 0. 6

3.2

Comparison to the RGS mo del of AU Microscopii

In the right panel of Fig. 4 we show the Au Microscopii MOS 2 sp ectrum in Timing Mo de and the data/mo del ratio when the b est-fit RGS mo del is applied in the 0.3­2 keV energy band. The three colors indicate the nominal sp ectrum (red), and the sp ectrum to whose resp onse matrix an energy-dep endent offset (black), and a linear gain correction (blue) had b een applied. Only an overall normalization factor C was allowed to b e free in the fit together with the Xspec gain fit parameters. The improvement from the first to the other two cases is evident. The corresp onding gain fit parameters are shown in Tab. 4. A nominal shift of 19 eV is required for the optimal alignment b etween the RGS b est-fit mo del and the energy as measured by the MOS2 camera. Such an offset is mainly driven by the Oviii Ly-, Neix He- and Nex Ly- emission lines. The observed difference is unaffected by the systematic uncertainties of the RGS wavelength scale (0.7 meV at the Oviii energy).

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MOS1 exp osures in Timing Mo de after Rev.#961

A new hot column app eared on MOS 1 CCD1 in Rev.#961 due to a micro-meteoroid event (Guainazzi 2009). The p ost-impact offset value in MOS1 Timing Mo de is far to o large for a meaningful correction to b e p ossible. Users are advised to discard the affected column (which in Timing Mo de


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calibrated event lists corresp onds to RAWX=319) and the adjacent ones from the accumulation of any scientific pro ducts. Users are referred to the watchout item at: http://xmm2.esac.esa.int/sas/8.0.0/watchout/Evergreen tips and tricks/mos1 timing.shtml, which outlines the SASv8.0-compliant pro cedure to generate a correct effective area file in these cases.

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Summary and conclusions

This rep ort investigates the accuracy of the energy reconstruction in MOS Timing Mo de exp osures, by comparing the centroid energies of strong atomic transitions in line-rich SNRs and star sp ectra against the measurements of the same lines in imaging mo de EPIC or RGS exp osures. The distribution of the centroid energy differences b etween measurements in EPIC-MOS Timing Mo de and EPIC-MOS or EPIC-pn in imaging mo de is 30 eV ( 20 eV) in N132D (CasA). Occasional discrepancies up to 40 eV are observed at the iron line energies in MOS 2, which will deserve further investigation. These results are confirmed by the direct comparison b etween the EPIC-MOS2 and RGS sp ectra of AU Microscopii, which requires an energy-indep endent shift of the MOS2 resp onse by 19 eV to b e aligned with an RGS-based phenomenological mo del.

Acknowledgments
Careful reading and detailed comments by M.Santos­LLeo and S.Sembay on an early version of this manuscript greatly improved the quality of the analysis and its presentation.

App endix A
The mo del used to phenomenologically fit the RGS sp ectrum of AU Microscopii is shown b elow (in compact Xspec jargon):

model

wabs(bremss + 17*gaussian) 0.00887249 0.001 0 0.820706 0.05 0.0001 0.0105081 0.01 0 1.021 1e-05 0 0 -1 0 0.000516254 1e-06 0 0.9175 1e-05 0 0 -1 0 1.27194e-05 1e-06 0 0.915 1e-05 0 0 -1 0 0.000107945 1e-06 0 0.922 1e-05 0 0 -1 0

0 0.0001 0 0 0 0 0 0 0 0 0 0 0 0

100000 100 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10

1e+06 200 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20


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0.000370232 0.905 0 0.000273348 0.8725 0 0.000191336 0.825 0 0.000277688 0.8175 0 8.71875e-05 0.812 0 0.000101719 0.77 0 5.21715e-05 0.774439 0 0.000242041 0.738854 0 0.000131671 0.726698 0 0.00035069 0.654 0 0.00125406 0.573998 0 0.000389254 0.561269 0 0.000287203 0.367616 0 0.000524661

1e-06 1e-05 -1 1e-06 1e-06 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06 1e-05 -1 1e-06

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24 1e+06 10 1e+24

1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 10 1e+24 1e+06 20 1e+24 1e+06 20 1e+24 1e+06 20 1e+24

References
Bleeker et al., 2001, A&A, 365, 242 Gabriel C., et al., 2003, ASCA, 314, 759 Gonz´ alez-Riestra R. & Ro dr´ iguez-Pascual P., 2008, Pro ceedings of the Workshop "Astronomical Sp ectroscopy and Virtual Observatory", Eds.: M.Guainazzi & P.Osuna, 37 Guainazzi M., 2009, "EPIC Calibration Status Do cument", XMM-SOC-CAL-TN-0018
2

2

available at: http://xmm2.esac.esa.int/docs/documents/CAL-TN-0018.pdf


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